This is very good to know that you are so serious about your Gate preparation but as per my view it is better to start your preparation in your 3rd year because first 2 years of B.Tech is the ideal time to make all your basics concept clear and strong. Apart from this, below I am providing Gate preparation tips which you should keep in your mind whenever you start your preparation  - 1. Know the syllabus very well as this is the first step and you will have to understand what you are up against and this information you need before you plan and then begin the actual preparation.
2. Read standard books only as there are many books available in the market so it is advisable to use the books which make all your concepts clear and which are easy to understand.
3. Understand the weight age of topics properly and accordingly devote time because I wont suggest you to give more time to those topics which has less weight age but those topics should not be ignored.
4. Proper Revision plan should be followed as this would be helping you a lot.
5. Mock Tests and Practice Tests should be done as this will help you to learn time management skills and this will also make you familiar with the exam pattern. Also, to make the best use of mock tests, better to check test analysis report properly as this will show where all you are still lacking or where all you have to work really hard.

Good Luck!!!